E.S.R. Studies of Halogenated Pyrimidines in Gamma-irradiated Alkaline Glasses

Simpson, Larry D.; Zimbrick, John D.

doi:10.1080/09553007514551291

Cited by 13 publications

(4 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It was concluded that the sensitivity of the halouracils to low-energy electrons is in the order BrU ≈ ClU ≫ FU. These findings are in agreement with experimental observations. ,− …”

Section: Introductionsupporting

confidence: 92%

“…These findings are in agreement with experimental observations. 7,[12][13][14][15][16][17][18] Since most experimental and theoretical studies focus on single halouracils, rather than on their pairs with adenine, one may wonder about the impact of the base pair configuration, which better mimics the environment in double-stranded DNA, on the radiosensitization properties. In the present work, we extend our previous density functional theory (DFT) investigations 8 to include the base pair partner adenine.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

DFT Investigation of Dehalogenation of Adenine−Halouracil Base Pairs upon Low-Energy Electron Attachment

Sevilla

Sanche

2003

J. Am. Chem. Soc.

View full text Add to dashboard Cite

The energetics of the dehalogenation of adenine-halouracil base pairs (A5XU), upon attachment of low-energy electrons, was investigated by use of density functional theory. These results are compared to those of single halouracils reported previously [J. Phys. Chem. A 2002, 106, 11248-11253]. Using the B3LYP functionals it was found that the gas phase adiabatic electron affinities (EA) of halogenated base pairs (A5BrU 0.59, A5ClU 0.56, A5FU 0.47 eV) are higher than that of AU (0.32 eV) and are slightly higher or comparable to the other DNA abundant base pair, guanine-cytosine (0.49 eV). Base pairing with adenine slightly decreases the EA of the halouracils, in contrast to the substantial increase in EA on base pairing of natural bases; as a result, the probability of electron capture by halouracils when in double-stranded DNA is suggested to be substantially reduced relative to that in single-stranded DNA. Even though the activation barriers for dehalogenation are small for both BrU-A and ClU-A, only the former has negative values of both DeltaH (-0.95 kcal/mol) and DeltaG (-1.52), while the latter has negative DeltaG (-0.28) but positive DeltaH (1.27). Infinite separations into halogen anions plus the remaining A-U-5-yl neutral radical are energetically unfavorable owing to sizable halide ion, radical interactions as reported earlier for non base paired halouracils. It is found that base pairing does not change the reactive nature of the uracil-5-yl radical. The results suggest that the radiosensitization properties of halouracils should be less effective in double-stranded DNA than in single-stranded DNA.

show abstract

“…It was concluded that the sensitivity of the halouracils to low-energy electrons is in the order BrU ≈ ClU ≫ FU. These findings are in agreement with experimental observations. ,− …”

Section: Introductionsupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

DFT Investigation of Dehalogenation of Adenine−Halouracil Base Pairs upon Low-Energy Electron Attachment

Sevilla

Sanche

2003

J. Am. Chem. Soc.

View full text Add to dashboard Cite

show abstract

“…In gas 9 and solid 13 phase experiments, it has recently been shown that nonthermalized low-energy secondary electrons (LEE), which are produced in abundance by high-energy radiation, are captured by the halouracils to form the transient anion. Metastable anion radicals of BrU or ClU were found to exist at low temperatures from ESR experiment; they undergo dehalogenation on temperature rise or light exposure. 11a,, …”

Section: Introductionmentioning

confidence: 99%

“…A variety of experiments have shown that halogen anions and uracilyl radicals are the products of the interaction of high-energy (MeV) electrons, γ-ray, subionization (0−10 eV) electron beams, ,, or X-ray 13 with halouracils and halogenated DNA. Several dissociation pathways have been proposed 12a to explain the fragmentation of halouracils after reaction with the electron.…”

Section: Introductionmentioning

confidence: 99%

Dehalogenation of 5-Halouracils after Low Energy Electron Attachment: A Density Functional Theory Investigation

2002

View full text Add to dashboard Cite

In this density functional theory investigation of the radiosensitization properties of 5-halogen-substituted uracils, the potential energy surfaces of the halouracils before and after electron attachment are investigated. The electron affinities (EA's) of uracil, halouracils, and uracilyl radical (U-yl • ) are calculated. The gas-phase adiabatic EA's of the halouracils after zero point energy (ZPE) corrections are in good agreement with those reported recently (Wetmore, S. D.; Boyd, R. J.; Eriksson, L. A. Chem. Phys. Lett. 2001, 343, 151-158). The U-yl • radical has an exceptionally high AEA of 2.34 eV and proton affinity of 9.5 eV in the gas phase, showing its reactive nature and potential to cause DNA damage when incorporated in the genome. The higher EA of the halouracils compared to that of the DNA bases supports the experimental reports on the increased probability of low-energy electrons to localize on halouracils in DNA, leading to dehalogenation reactions and DNA damage. Potential energy surfaces (PES) are calculated for dehalogenation to show the relative energy change in the dissociation of halogen from both the neutral molecule and anion radical. The PESs along the C 5 -X bond of all neutral molecules including uracil show the typical surface expected for a strong covalent bond rupture. Each of the halouracil anion radicals is found to have two thermally accessible electronic states of differing symmetries, i.e., π*(A") and σ*(A ' ), that have quite differing properties. Both the pure π* state and the σ* state feature planar geometries. The pure π* state has a PES similar to that of the neutral molecule with a strong C-X bond, while the σ* state shows far weaker C-X bonding. Moreover, there is a mixed state PES that undergoes a transition from a slightly nonplanar π* state to that of a σ* state as the C-X bond distance increases to the crossing point of the two PES. From the full PES that allows for state crossing, the lowest energy barriers for formation of the extended σ* states are estimated to be 20.80, 3.99, and 1.88 kcal/mol for F-, Cl-, and Br-substituted uracil anion radicals, respectively. The overall energetics suggest that the π* to σ* conversions are exothermic for ClU and BrU anions, with ∆H calculated to be -0.98 and -2.98 kcal/mol, ∆G, -2.32 and -3.80 kcal/mol at 298 K and 1 atm, respectively. Remarkably, for the F-U anion the lowest energy path is not the loss of fluoride ion but the detachment of HF. The sensitivity of the halouracils to low-energy electrons is found to be on the order of BrU ≈ ClU . FU, in agreement with experimental observations.

show abstract

Low‐Energy Electron Interaction with DNA: Bond Dissociation and Formation of Transient Anions, Radicals, and Radical Anions

Sanche

2009

Radical and Radical Ion Reactivity in Nucleic Acid Chemistry

173

View full text Add to dashboard Cite

E.S.R. Studies of Halogenated Pyrimidines in Gamma-irradiated Alkaline Glasses

Cited by 13 publications

References 15 publications

DFT Investigation of Dehalogenation of Adenine−Halouracil Base Pairs upon Low-Energy Electron Attachment

DFT Investigation of Dehalogenation of Adenine−Halouracil Base Pairs upon Low-Energy Electron Attachment

Dehalogenation of 5-Halouracils after Low Energy Electron Attachment: A Density Functional Theory Investigation

Low‐Energy Electron Interaction with DNA: Bond Dissociation and Formation of Transient Anions, Radicals, and Radical Anions

Contact Info

Product

Resources

About